The Joint Meeting of 5th IAEA Technical Meeting on Spherical Tori, 16th International Workshop on Spherical Torus (ISTW2011), and 2011 US-Japan Workshop on ST Plasma September 27-30, 2011 , National Institute for Fusion Science, Toki, Japan Recent Progress in the SUNIST Spherical Tokamak Yi Tan1, Zhe Gao1, Wenhao Wang1, Lifeng Xie1, Long Zeng1, Huiqiao Xie1, Ou Zhao1, Yangqing Liu1, Yanzheng Jiang1, Song Chai1, Xiaowei Peng1, Kun Yao1, Aihui Zhao1 Chunhuan Feng2, Long Wang2, Xuanzong Yang2 Guixiang Yang3 Email: [email protected] 1) Department of Engineering Physics, Tsinghua University, Beijing, China 2) Institute of Physics, Chinese Academic of Science, Beijing, China 3) College of Nuclear Physics and Technology, Nanhua University, Hengyang, China This work is supported by the Major State Basic Research Development Program from MOST of China under Grant No. 2008CB717804, 2009GB105002 and 2010GB107002, NSFC under Grant No. 10990214, 10775086 and 11005066. Introduction to SUNIST • SUNIST: Sino UNIted Spherical Overview of the SUNIST device Tokamak – What are united? • Department of Engineering Physics, Tsinghua University • Institute of Physics, Chinese Academy of Sciences – Major parameters • R0/a: 0.3/ 0.23m ~ 1.3 • BT0: <0.15 T • IP: ~ 50 kA 19 -3 • ne: ~ 110 m – Major diagnostics • Langmuir probes • Normal ( <100 kHz) / High frequency (~1 MHz) magnetic probes • Visible Spectrometers (250~ 750 nm) • 94 GHz interferometer • 8 mm reflectometer • Fast visible camera • Ha diode array Section view of the The vacuum SUNIST device vessel of SUNIST 2011-9-29SUNIST 2 Major Research Interests of SUNIST • Non-inductive current startup and drive – Startup: by electron cyclotron waves (ECW) • Breakdown the neutral gas and initiate a small plasma current – Drive: by Alfven waves (AW) • Maintain the ohmic plasma current total IP IP started up IP by ECWs An idealized running scheme for SUNIST IP ramped IP driven up by the by AWs solenoid O t startup ramp up sustain • Properties of ST plasmas – Edge plasmas • Electrostatic/magnetic fluctuation and anomalous transport characteristics – MHD characters • MHD behaviors and methods to affect or control MHD activities 2011-9-29SUNIST 3 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary 2011-9-29SUNIST 4 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary 2011-9-29SUNIST 5 Analysis of ECW startup • Brief experimental results of (a) (b) (c) (d) (e) (f) ECW startup st – 2.45 GHz/100 kW/10 ms (limited) 1 t ECR shot 070930.14 h g i ) l . 1 (g) l u l – O mode outboard injection . a a r ( e 0 v – ~2 kA I last for several ms o P 100 n o i (h) ) t c 50 – I is inversely proportional to B % e P V ( l f e – Closed flux surface may formed but r 0 ) 2 (i) A no current jump observed k ( 1 p I 0 • What we focused on 6 8 10 12 14 – The spikes at the beginning of time (ms) Typical waveforms of ECW startup on SUNIST discharges (IP,Ha and ne) 2.45 GHz, ~20kW – The time and spatial evolution of0.9 n dl (1017m-2), L0.6m n is essential to understand the 0.6 e (a) e 0.3 physics of startup 0 2 H emission(a.u.) Shot 060413.6 – Investigate the transient 1 (b) process of the plasmas during 0 13 15 17 19 21 23 25 startup ! Time (ms) – PS: spikes are widely found on STs Spikes are found at the beginning of discharges 6 Effects of BV,BT and Prf on the spikes Bv = 59 G ) Bv = 37 G . 2 (a) u . Bv = 20 G a ( n o 1 i s s i m e 0 H 6.4 6.6 6.8 Time (ms) (b) Bv = 59 G 1 ) . u e . v a 0 Bv = 37 G ( B scanning results a T 1 n w o o i r t c c i 0 e l f M 1 e r Bv = 20 G 0 6.0 6.5 7.0 7.5 8.0 Time (ms) BV scanning results • Ha and the reflected microwave are found to have connections with these scanning parameters – These two signals are fast enough to be able to catch the details of changes Prf scanning results 2011-9-29SUNIST 7 Conjectures from the scanning results Summary of the scanning results +: positive effects, -: negative effects; 0: no effects Slew rate of the Delay Maximum Amplitude reflected rf of Ha amplitude of of the flat power peaks Ha top of Ha BT + - 0 0 BV - 0 - 0 Prf 0 - + 0 Drift/Formation Power Ionization Conjectured Microwave time of the cut density rate and loss explanations frequency off layer @ ECR rate 2011-9-29SUNIST 8 The physical image of the initial stage of ECW startup • Main processes – Ionization by microwaves – Reflection of microwaves – The motion of particles: (1) drift and diffusion across the field lines, (2) parallel motion along field lines • Features of our experimental arrangements – Perpendicular installation of the horn antenna • The antenna acts not only as a launcher of power microwaves but also a receiver of reflected microwaves 2011-9-29SUNIST Tan Y, et al. Nuclear Fusion. 2011;51(6):063021. 9 Estimation of the speeds • For electrons (100 eV) – Lamor Radius: ~ 0.4 mm (v// = 0, B = 875 G) – v//: ~6E6 m/s ( ) • For hydrogen gas (300 K, 1E-3 Pa) ⊥ – en: ~3E4 1/s (3E9 1/s for 1 torr) – ionization: ~2E4 1/s (2E9 1/s for 1 torr) – ei: ~ 1E3 1/s (ne ~ 1E17) • For SUNIST (R0 =0.3m,B=875G) – R : ~ 7.6E3 m/s (vertical) ଶ் ଵ – ߘܤ: ~1.1E3 m/s஼ (E = 100 V/m) (radial) × ௤ ோ ஻ ୉ – ܧ ܤ : ~ 1.4E5 m/s (B = 20 G) (vertical) V ୆ z ஻௭ ∥ ஻் 2011-9-29SUNIST 10 Modeling Cutoff layer nk W L kECR i2k 1 PP e nc (5) kECR inj Horn antenna 2d tan W 2d tan L k k ANT 2 2 W W L r REF 4d tan W 4d tan L 2 2 (4) nk 2 D n D n L n G n n ()k kECR (1) d t DIFF k DRIFT k BV k ECRkNP nk 2 (2) D n D n L n ()k k ECR t DIFF k DRIFT k V k n n 1 NP k (3) t t N • A 1.5 dimension model – To describe the main processes – To simulate the time and spatial evolution of ne, the characters of microwave reflections – Approximations: optical launch and receive, WKB et al. 2011-9-29SUNIST 11 n e 10 0 5 0 x 10 2011-9-29 12 H (a.u.) Compare the simulations and the experiments (b) 12 Reflection (a.u.) 0 1 2 6.0 6.5 7.0 7.5 8.0 0.5 (a) Time (ms) One spike Oscillating B Time (ms) H 1 1.5 Reflection 2 0 0.02 0.04 Reflection (a.u.) n Reflection H Reflection e (%) (a.u.) 0 1 2 3 4 (%) 20 40 60 20 20 40 60 0 0 0 x 10 8.0 8.5 9.0 9.5 10.0 2 4 6 8 10 12 14 16 (a) Experimental results: (b) (c) 11 Reflection 0.5 Simulation results Time (ms) shot 060927.6 Time (ms) SUNIST 1 1.5 (d) H Tan Y, et al. Plasma Sci. Tech. 2011;13(1):30. 2 0 0.01 0.02 0.03 0.04 10 20 30 H (a.u.) Reflection (a.u.) Due to: Reflection Ratio N 0.1 0.2 0.3 0.4 e 10 0 5 Reflection (a.u.) 0 H (a.u.) x 10 a 20 40 0 4 8 0 (d) 12 100 (b) 2.0 2.2 2.4 2.6 (a) 200 T scanning 300 Time (ms) 400 Time (a.u.) Time (us) (c) 500 600 R R R R 700 ECR ECR ECR ECR = R = = R = R R 0 0 0 0 - + 7 cm + 4 cm + 1 cm 800 5 cm 950 G 850 G 750 G 650 G 900 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary 2011-9-29SUNIST 13 Principle of Alfven wave current drive • Diagram of Alfven wave current drive (AWCD) – The peristaltic Tokamak (Wort, 1971) dv B The driving force: m z eE z dt z z v e vf )( Resonant Vph is slow thus thermal condition： electrons are driven: vk e 0 v T v N J Fisch and C F F Karney, 1987 The schema: Vacuum Vessel • Apply AWCD to SUNIST Antennas Plasmas – 4 pairs of strap antennas – 0.15T/ 1E19m-3, resonant frequency: 0.4 ~ 1 MHz Alfven wave antenna design for SUNIST • Simple design, simple manufacture – Extends in the poloidal direction as much as possible 50 mm bolts bolts BN plates returning strap main strap Support for BN plates feeder CF-200 flange 150 mm 2011-9-29SUNIST Tan Y, Gao Z, He Y. Fusion Eng. Des. 2009;84(12):2064-71.15 Preliminary results of AW experiments • Antennas antennas – Currently no shielding, no limiters – Two of four pairs used – phasing – |N|=1 ~ 60%, |M|=1 ~ 15% • The RF generator – Four phases outputs Toroidal arrangement of the antennas(left) and a picture • But only two phases are stable of the antennas along with plasmas (right) – 20 ~ 50 kW, 0.4 ~ 1 MHz (non-continuous) • Experimental parameters – IP：30~50 kA -3 – ne： 0.5 ~ 319 m – BT：800~1200 G • Antenna impedances – Have similar trends as 1-d calculations Experimental results (left) and theoretical results (right) of the impedances of antennas 2011-9-29SUNIST 16 The effects of RF waves on IP Runaway discharges • Runaway discharges are enhanced when: – Low IP (~30 kA), low ne (<1E19 m-3) – Hard to understand • The speed of rf phases and the runaway electrons differ by one order of magnitude -2 • Vc～1.5*10 (2πRn/V)/2 ～ 7 18 -3 Normal discharges 2*10 m/s (for ne～10 m ) • Vph～f2 π R ～ 1.5*106 m/s • Normal discharges – 50 kA，>1E19 m-3 – No effects observed 2011-9-29SUNIST 17 Outline • Recent research progress – Analysis of the startup by ECWs – Preliminary results of AW experiments – MHD studies • Recent engineering progress – Upgrade of the field power supplies – Other upgrades • Future plans • Summary 2011-9-29SUNIST 18 Internal reconnection events on SUNIST • Motivations – Internal reconnection events (IREs) are widely found on STs – What mode structures do IREs have? – The evolution of equilibrium parameters during an IRE • Methods – Magnetic measurements A typical discharge with IREs of SUNIST – EFIT – SVD analysis 0.5 0.4 0.3 0.2 0.1 ) m 0 ( Magnetic probes (*) and flux Z loops (.) used to study MHD -0.1 activities on SUNIST -0.2 -0.3 -0.4 -0.5 Zoomed in waveforms of IP and magnetic perturbations 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 of an IRE R (m) 2011-9-29SUNIST Zeng L, et al.